Optical disc apparatus

ABSTRACT

An optical disc apparatus includes a pause circuit for pausing data encoders upon receiving a pause signal so that a write operation may be paused without writing dummy data, thereby maintaining data succession. The optical disc apparatus also includes a circuit for accurately determining a write start location by referring to previously written data. A processor generates a pause signal when the amount of data in the optical drive apparatus data buffer is low, and removes the pause signal when additional data from a host is received. The processor may also automatically reduce the write speed of the optical disc apparatus upon a pause condition, thereby preventing the necessity for excessive pausing.

This application is a divisional of application Ser. No. 10/129,042,filed Jul. 22, 2002 now U.S. Pat. No. 6,661,755; which is a continuationof application Ser. No. 10/082,345, filed Feb. 26, 2002 (now U.S. Pat.No. 6,570,832); which is a continuation of application Ser. No.09/741,900 filed Dec. 22, 2000 (now U.S. Pat. No. 6,418,099); which is acontinuation of application Ser. No. 08/906,290 filed Aug. 5, 1997 (nowU.S. Pat. No. 6,198,707). Each of these applications and patents areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical disc drive which records andreproduces information for an optical disc like a CD-R media or a CD-RWmedia.

2. Description of the Related Art

The recording format of a CD-R or CD-RW optical disc is prescribed inthe Orange Book, an industry standard. The Orange Book rules dictatethat data sectors which are not consecutively written require lengthylead-in and lead-out sectors such as Link, Run-In, and Run-Out sectors.These sectors are necessary to enable optical disc drives to synchronizeto the data on the optical media. This is because the laser beam must berepositioned each time a new writing session is started, and knownoptical disc drive positional controls are not sufficiently accurate toposition a laser beam at the exact end point of previously written data.

Therefore, conventional optical disc drives need to write data on anentire track, known as Track-at-Once, or an entire disc, known asDisc-at-Once, continuously in order to avoid adding lead-in and lead-outsectors. In other words, known optical disc drives must write the entiredisc or track in a single writing session.

Conventional optical disc drives employ Cross-Interleaved Reed-SolomonCode (CIRC) encoding which is performed by a CD encoder chip. The CDencoder chip automatically encodes the data in a buffer whichtemporarily stores data from a host while waiting for the data to beencoded and written to an optical media. Another reason thatconventional optical disc drives must write data in a single session isthat the CD encoder chip will continue to generate dummy data even ifthe buffer containing data from the host becomes empty. Continuity ofdata, or data succession, is lost by inserting and writing dummy data ina head where data from a preceding sector was recorded.

Because conventional disc drives need to write an entire track or discin a single session, a problem is encountered if the flow of data fromthe host computer to the optical disc drive buffer is interrupted. SinceCD-R and CD-RW optical discs are write-once media, a write failureresults in the loss of expensive media.

The problem of maintaining data from the host in the optical disc drivebuffer is severe when the writing speed of the optical disc drive ishigh. Because the data size of a track or disc is large compared to theoptical disc buffer size, if the data transfer rate between the hostcomputer and the optical drive is even slightly slower than the speed atwhich data is written to the optical disc, or data transfer between thehost and the optical disc drive is interrupted for even a short period,the buffer may go empty. This problem is known as Buffer Run.

Because hosts transmit data at varying rates, some optical disc drivesinclude a test mode that performs a dummy write operation, during whichno data is actually written to the optical disc, to ensure that thetransmission rate of the host is adequate to prevent buffer run. Oneproblem with this method is that it takes twice as long to write thedata to the disc. Also, because hosts sometimes encounter non-repeatableproblems, the aforementioned method is not perfectly safe and the riskof losing expensive media due to buffer run errors is not completelyeliminated.

Therefore, an optical disc drive that can write data consecutively andnormally to an optical media in multiple sessions without the loss ofdata succession is needed.

Even if logical data succession is ensured as described above, datacannot be normally reproduced without physical correspondence of thesucceeding portions of data written in multiple sessions.

Usually, a frame gap of up to +/−2 bits may be present withoutpreventing a conventional optical disc drive from properly reproducingdata from an optical disc. However, if a conventional optical disc driveattempts to write multiple sessions of data by selecting a writing startpoint based on a rotating control by a wobble synchronic signal, a framegap of scores of bits may result. Therefore, synchronization may be offin that portion and several frames of data may be lost.

Therefore, what is needed is an optical disc drive that is able tocorrectly detect an end portion of data written in a preceding writesession so that an accurate write start point is provided for asucceeding write session.

Further, it is desirable that such an optical disc drive should be ableto detect the end portion of data written in a preceding write sessionat low cost.

SUMMARY OF INVENTION

An object of the present invention is to provide an optical discapparatus characterized by writing means for maintaining data successionby halting CIRC encoding at the end of a preceding write session andresuming CIRC encoding at the beginning of a succeeding write session.

A second object of the present invention is to provide an optical discapparatus characterized by a counter circuit for counting the channelbit PLL (phase locked loop) which takes timing from the end ofpreviously written data to select a writing start point for a succeedingwrite session.

A third object of the present invention is to provide a counter circuitfor counting a frame sync signal which takes timing from the end ofpreviously written data to select a writing start point for a succeedingwrite session.

A fourth object of the present invention is to provide controlling meansfor controlling the writing of data to an optical disc drive accordingto the present invention. The controlling means pauses a write operationwhen data from the host has not been transmitted in time for writing tothe optical disc, and restarts the write operation when data from thehost computer is again available.

A fifth object of the present invention is to provide an alternatecontrolling means for controlling the writing of data to an optical discdrive according to the present invention. The alternate controllingmeans pauses a data write operation when data from the host has not beentransmitted in time for writing data to the optical disc, reduces thewrite speed of the optical disc drive, and then resumes the writeoperation.

In accordance with the first object, the optical disc drive includes aPause circuit which masks the clock input to the encoders upon thegeneration of a Pause signal. This prevents the encoders from furtherinputting and outputting data. Therefore, even if writing to the opticaldisc occurs in multiple write sessions, data succession is maintained.

In accordance with the second object, one embodiment of an optical discdrive according to the present invention includes a counting circuitwhich counts the PLL signal derived from the channel bit. The PLL signalhas the smallest error for previously written data. It is possible tocalculate the end of the data based on this signal, so that the correctwriting start point for succeeding data write sessions may be selected.

Many inexpensive and widely used decoder LSIs which are used in knownoptical disc drives do not output a channel bit PLL, but rather output aframe sync signal and a sub code sync signal as a sub code output.Therefore, in accordance with the third object, a second embodiment ofan optical disc drive according to the present invention includes acounting circuit which counts a frame sync signal and a sub-code syncsignal to select a writing start point for a succeeding data writesession. Accordingly, it is possible to detect the end of the previouslywritten data at low cost.

In accordance with the fourth object, one embodiment of an optical discdrive includes a processor for detecting when data from a host stored ina data buffer is low, generating a pause signal for pausing a datawriting operation, waiting until additional data is received from thehost, and removing the pause signal so that the data writing operationmay resume.

In accordance with the fifth object, another embodiment of an opticaldisc drive includes a processor for detecting when data from a hoststored in a data buffer is low, generating a pause signal for pausing adata writing operation, decreasing the write speed of the optical discdrive, and removing the pause signal so that the data writing operationmay resume.

Because an optical disc drive according to the present invention canwrite in multiple sessions, a data interruption between the host and theoptical disc drive does not result in the loss of the media, therebyreducing the cost of operating the optical disc drive. Accordingly, alarge data buffer is not necessary, which also lowers the cost of theoptical disc drive. This ability to write in multiple sessions alsoeliminates the need for a test write operation to test the transmissionrate of the host computer, which saves time. It is also unnecessary fora user to be aware of the transmission rate of the host and the writerate of the optical disc drive, which simplifies operation of theoptical disc drive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a hardware block diagram showing the structure of an opticaldisc apparatus in accordance with one embodiment of the presentinvention.

FIG. 2 is a format diagram showing the format of CD-R or CD-RW data onan optical disc.

FIG. 3 is a timing diagram showing an example of a possible timingsequence of plural write sessions for writing data in the format shownin FIG. 2.

FIG. 4 is a circuit diagram of a write control circuit in the opticaldisc apparatus of FIG. 1.

FIG. 5 is a format diagram showing the positional relationship of theend data written in a preceding write session and start data written ina succeeding write session by a conventional optical disc apparatus.

FIG. 6 is a format diagram showing the positional relationship of theend data written in a preceding write session and start data written ina succeeding write session by optical disc apparatus according to thepresent invention.

FIG. 7 is a circuit diagram showing a circuit for generating a writestart signal at the end of previously written data, as shown in FIG. 6,according to one embodiment of the present invention.

FIG. 8 is a timing diagram showing the write timing of an optical discdrive using the circuit of FIG. 7.

FIG. 9 is a circuit diagram showing a circuit for generating a writestart signal at the end of previously written data, as shown in FIG. 6,according to a second embodiment of the present invention.

FIG. 10 is a timing diagram showing the write timing of an optical discdrive using the circuit of FIG. 9.

FIG. 11 is a flow chart showing one method for writing data to anoptical disc using an optical disc drive according to the presentinvention.

FIG. 12 is a flow chart showing a second method for writing data to anoptical disc using an optical disc drive according to the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the accompanying drawings.

FIG. 1 is a hardware block diagram showing the structure of an opticaldisc apparatus according to one embodiment of the present invention. Theoptical disc 1 is turned by the spindle motor 2. The spindle motor 2 iscontrolled so as to keep constant linear velocity by the motor driver 3and the servo 4. The linear velocity can be changed stepwise. Theoptical pick-up 5 includes a semi-conductor laser, an opticalarrangement, a focus actuator, a photo detector, and a position sensor.The optical pick-up radiates laser rays L on the recording surface ofthe optical disc 1.

The optical pick-up 5 can be moved in a seeking direction. The focusactuator, track actuator, and seek motor are controlled to locate andfocus the laser beam L on a target point of the optical disc 1 by themotor driver 3 and the servo 4 based on signals from the photo detectorand position sensor of the optical pick-up 5.

When reproducing data, a reproducing signal obtained from the opticalpick-up 5 is amplified and digitized by the read amplifier 6 and inputto the CD decoder 7, where de-interleave and error correction arecarried out.

When the reproduced data is audio or music data, an analog audio signalis derived by inputting the output data from the CD decoder 7 into theD/A converter 12.

When the reproduced data is ROM data, the de-interleaved anderror-corrected data from the CD decoder 7 is input to the CD-ROMdecoder 8, and further error correction is carried out. After that,output data from the CD-ROM decoder 8 is stored in the buffer RAM 10 bythe buffer manager 9. When a complete sector of data is ready, the datais transferred to the host computer by the ATAPI/SCSI interface 11.

When data is to be written to the optical medium 1, the laser beam mustbe positioned at the writing start point. The writing start point issearched by the wobble signal pressed beforehand in the form ofmeandering track. The wobble signal includes absolute time informationcalled ATIP. The ATIP information is derived by the ATIP decoder 13. Asynchronizing signal produced by the ATIP decoder 13 is input to the CDencoder 14, and it is possible to write data at an accurate position.

Data that is to be written to the optical disc 1 is received from thehost computer through the ATAPI/SCSI interface 11. The data is stored inthe buffer RAM 10 by the buffer manager 9.

Data writing begins once data is present in the buffer RAM 10. Errorcorrection codes are added to the data, and CIRC encoding is performed,by the CD-ROM encoder 15 and/or the CD encoder 14. The data is recordedon the target optical disc 1 through the laser control circuit 16 andthe optical pick-up device 5.

Known optical disc drives cannot immediately begin reading User DataBlocks on an optical disc drive. In order for an optical disc drive toachieve synchronization and data interleave, lead in and lead out blocksare necessary. FIG. 2 shows a format that provides five lengthy lead inblocks comprising a link block and Run In Blocks 1-4 preceding the UserData Block, and two lengthy lead out blocks comprising Run Out Blocks 1and 2 after the User Data block.

In order to prevent the aforementioned Buffer Run problem, the opticaldisc apparatus of the present invention is capable of writing user datain multiple write sessions. FIG. 3 illustrates an example of writingdata in the format shown in FIG. 2 in multiple write sessions. Theoptical disc drive of the present invention receives data from the hostcomputer, and carries out Start Write when the buffer RAM 10 is full ofdata. Start Write includes writing the lead-in and run-in blocks shownin FIG. 2.

When the optical disc drive starts to write the User Data Block, thedata remaining in the buffer RAM 10 is reduced. If the amount of data inthe buffer RAM 10 is below a preset level, a Pause signal is generatedand the writing stops. The optical disc drive then waits for additionaldata transmission from the host. When the buffer RAM 10 is again full,Restart Write is carried out by removing the Pause signal and data iswritten from the position at which the writing was paused. When all datafrom the host computer is written to the optical disc 1, the Stop Writepoint is reached.

A conventional optical disc drive cannot write data in theaforementioned manner for two reasons. First, a conventional disc drivedoes not provide a mechanism for stopping the CD-ROM encoder 15 and CDencoder 14 (FIG. 1) when no data is present in the buffer RAM 10. Thus,when no data is present in the buffer RAM 10, the encoders continue towrite data, which changes the data format unit actually written on theoptical disc 1 from the logical data format received from the host.

The logical data format unit must conform, as prescribed by the OrangeBook, to the physical data format unit on the optical disc. If theencoder could be made to stop when data is not present in the buffer RAM10, it would be easy to ensure that the physical data format units onthe optical disc 1 conform to the logical data format units from thehost.

FIG. 4 is a circuit diagram showing a circuit which controls datawriting by pausing the encoders when a pause signal, indicating that thebuffer RAM 10 is awaiting more data from the host, is received. When aPause signal is input to the circuit, the clock to the CD-ROM encoder 15and the CD encoder 14 is masked. Therefore, the CD-ROM encoder 15 andthe CD encoder 14 stop encoding and stop outputting Write Data.

The Write Gate signal is also masked by the Pause signal. Therefore,data writing for the optical disc stops also. The encoding data in theRAM 21, 22 is maintained during the Pause. Then, when the Pause signalis canceled, writing on the optical disc resumes with data successionmaintained. The pause signal is highly synchronized to the pausing andresuming of the data writing.

The second reason why a conventional optical disc drive cannot writedata in the manner described in FIG. 3 is that the writing start pointof the laser beam L cannot be controlled with sufficient accuracy usingspindle motor controls based on the ATIP of the wobble signal.

FIG. 5 is a format diagram showing the positional relationship of theend data written in a preceding write session and start data written ina succeeding write session by a conventional optical disc apparatus. Asshown in FIG. 5, a large data overlapping of 4 EFM (eight to fourteenmodulation) frames is possible with a conventional disc drive. Such alarge error can occur due to spindle motor controller errors. Thestarting position of the data writing in a conventional disc drive isselected based on the ATIP of the wobble signal without reference topreviously written data. When such a large error occurs, framesynchronization is out and it is impossible to reproduce data properlyeven for an optical disc such as a CD, which has high error correctioncapacity.

It is necessary, as shown in FIG. 6, to write succeeding data within a+/−2 bit clock error. Thus, it is impossible to accurately position thelaser beam to the correct start location using a conventional opticaldisc drive with writing control based on the spindle motor control.

In contrast to known optical disc drives, the optical disc drive inaccordance with the present invention locates the end of the datapreviously written. The end position is based on the clock used tosynchronize written data. The data writing start position is then basedon the end position.

FIG. 7 is a circuit diagram illustrating a circuit for generating awrite start signal at the end of previously written data (as shown inFIG. 6) according to one embodiment of the present invention. FIG. 8 isa timing diagram showing the write timing of an optical disc drive usingthe circuit of FIG. 7.

The circuit shown in FIG. 7 generates a write start signal by countingthe channel bit PLL signal. The channel bit PLL clock number from therising position of the sub code sync clock to the end position of dataframe 25 is set in the channel bit offset register 30. This number isdecided by sub sync clock producing timing (hardware) of the CD decoder.Therefore, the value of the channel bit offset register 30 cannotincrease and decrease dynamically. The CD encoder reads the sub code ofeach frame and produces the sub code sync clock. However, decode delayis a little different because of variable CD decoder chips. Therefore, agap between the data and the phase of the sub code sync clock isproduced. The channel bit offset register 30 adjusts the gap. Theapparatus detects the address of the writing start sector 1 by the ATIPor sub Q code, and loads the channel bit offset register 30 value to the16 bit down counter 31 on the first sub code sync, which is the sub-codesync of the writing start sector. The down counter 31 then decrements onsucceeding clock signals. Finally, when the 16 bit down counter 31reaches zero, it outputs RC (Reset Counter), which is used as the WriteStart signal.

Thus, it is possible to accurately start to write from the end of thedata written during the preceding write operation. The write startsignal for the succeeding portion of data with the smallest possible gapis formed by using the channel bit PLL, which is the signal with thesmallest error.

Many inexpensive and widely used decoder LSIs used in conventionaloptical disc drives do not output a channel bit PLL signal. Rather, aframe sync signal and a sub code sync signal are output by thesedecoders. It is also possible to use these signals to accurately beginwriting succeeding data at the end of previously written data.

FIG. 9 is a circuit diagram showing a circuit for generating a writestart signal based on the frame sync and sub code sync signals from thedecoder 7 of the optical disc drive shown in FIG. 1. FIG. 10 is a timingdiagram showing the relationship between the input frame sync and subcode sync signals and output write start signal obtained from thecircuit shown in FIG. 9.

The circuit shown in FIG. 9 generates a start write signal by countingthe frame sync clock. The frame offset register 40 inputs the frame syncclock number from the sub code sync clock to a Fr25 frame sync clock.The clock offset register 41 inputs the Write standard clock number fromthe Fr25 frame sync clock to the write start position.

Then, the address of the writing start sector 1 is detected by ATIP orsub code. The frame offset register value is loaded to the 5 bit downcounter 42 by the first sync code, which is the sub code sync of thewriting start sector. The channel bit offset register value is loaded tothe 16 bit down counter 31.

When the 5 bit down counter 42 is decremented by the frame sync clockand becomes zero, it loads the value of the clock offset register 41 tothe 11 bit down counter 43. When the 11 bit down counter 43 isdecremented by the Writing standard clock and becomes zero, it outputsRC, which is the Write Start signal.

In this manner, it is possible to start to write accurately from the endof previously written data based on a count of the frame sync signal.The frame sync signal can be obtained by an inexpensive and widely useddecoder LSI. Therefore, the cost of the optical disc drive can bereduced.

The CPU 17, ROM 18 and RAM 19 (FIG. 1) are used to control writeoperations for the optical disc drive according to one of two methods.One such method is shown in FIG. 11. When writing is to start, the linkblock and four run-in blocks are written to the disc at step S1. Userdata in the buffer is written to the disc as step S2. This is the normalwriting sequence which starts from the link and run-in blocks.Additional data is received from the host at step S3. At step S4, theamount of data in the buffer is determined to determine whether a bufferrun error may be occurring.

If the data in the buffer from the host is not low in step S4, thebuffer is checked to determine whether the data is complete at step S5.If data writing is not complete, the data writing continues at step S2.If the data writing is complete, Stop Write occurs at step S6, and thewrite operation is complete. Stop Write is normal sequence of writingthe Run out blocks.

If the data from the host is low in the step S5, a Pause Write signal isgenerated to pause the write operation at step S7 while more data isreceived from the host at step S8, thereby preventing a buffer runcondition. The content of the buffer is checked at step S9. If thebuffer is not full at step S9, additional data is received at step S8.When the buffer is full, writing resumes at step S10 without writing anylink blocks, thereby maintaining data succession. The writing operationcontinues at step S3.

In this manner, when the data transmission from the host is not in timeduring write operations to the optical disc, the data writing stops.When the data is fully sent from the host, the write operation resumes.

Accordingly, when the data transmission from the host is momentarilyinterrupted, or the transmission rate is reduced, it is possible towrite data on the optical disc by dividing the write operation into aplurality of write operations. Data writing failures can thus beprevented. The size of the buffer RAM necessary for absorbing datatransmission rate variations can therefore be reduced, thereby reducingthe cost of the optical disc drive.

A second method for controlling the write operation of an optical discdrive according to the present invention is shown in FIG. 12. In thismethod, the Start Write operation is carried out at the speed set by thehost, or at the maximum speed of the disc drive if no speed is specifiedby the host, at step S11. Data is written to the optical disc at stepS12. Additional data is received from the host at step S13. The amountof data in the buffer is determined at step S14. The buffer may becomedepleted for the reasons discussed earlier.

If the data in the buffer from the host is not low at step 14, it isdetermined whether the data has completed at step S15. If the data hasnot completed, data writing continues at step S12. If the data hascompleted, Stop Write is carried out at step S16 and the writingoperation is complete.

If the data from the host is low at step 14, a Pause Write is generatedat step S17 so that writing on the optical disc pauses. Then, additionaldata from the host is received at step S18. When the buffer is full atstep S19, the optical disc drive recording speed is lowered one step atstep S20 if the speed is not already at the minimum. The pause signal isremoved at step S21, and the write operation continues at step S13without writing any link blocks and maintaining data succession.

In this manner, when the data transmission rate from the host is lessthan the data writing rate of the optical disc, the data writing stops,the writing rate of the optical disc is stepped down, and data writingresumes.

Accordingly, the optical disc drive continues writing data afterautomatically changing the data writing speed in response to the datatransmission rate from the host. Therefore, it prevents excessively longdata writing operations caused by repeated Pauses. Further, a user doesnot have to check the data transmission capacity of the host and thewriting speed of the optical disc driver. Therefore, the write operationis simple, and it is possible to write the data at the maximum capacityof the host.

The entire disclosure of Japanese Patent Application No. 8-206705, filedAug. 6, 1996, is expressly incorporated herein by reference.

The above description and drawings are only illustrative of preferredembodiments which can achieve and provide the objects, features andadvantages of the present invention. It is not intended that theinvention be limited to the embodiments shown and described in detailherein. Modifications coming within the spirit and scope of thefollowing claims are to be considered part of the invention.

1. An encoding circuit for a CD-R or CD-RW recording apparatus, saidencoding circuit comprising: a first memory; a second memory; a CD-ROMencoder for generating first encoded data, said first encoded data beingstored in said first memory; and a CIRC encoder for generating secondencoded data, said second encoded data being stored in said secondmemory; and wherein said encoding circuit supports a pause conditionwhich pauses said CD-ROM encoder and said CIRC encoder while maintainingthe contents of said first and second memories.